The Moving Picture Experts Group (MPEG) is an ISO-promulgated group of standards. MPEG-2, the standard on which such products as digital television set top boxes and DVD are based, is a video encoding format that has become the standard for VoD service over cable video networks. The ISO's MPEG-2 Systems specification, incorporated herein by reference in its entirety, is designed for a network with constant end-to-end delay. MPEG-2 has a stringent timing requirement in the packet schedule and time stamps. It works well for some dedicated video networks such as ASI or IF/RF used in existing hybrid fiber coax (HFC) plants.
Recently, cable operators have adopted IP over Gigabit Ethernet (IP/GbE) technology for video distribution networks. IP/GbE offers many advantages over other transport technologies, such as lower cost, simplified network management, and flexibility for introducing new services. However, IP networks have an inherent problem of network jitter that violates the MPEG assumption on the underlying delivery mechanism. This problem needs to be solved before cable networks can deliver seamless video to subscribers.
While IP/GbE is used to distribute MPEG video from the headend to the distributed hub, the existing HFC plant is still used as the “last mile” delivery medium to subscribers. At the distribution hub, the video data first is IP depacketized, then remuxed, modulated and upconverted for transmission on the HFC network to the subscriber's set top box. During this transition, network jitter introduced by the IP has to be removed. In addition, due to the remixing process, in which multiple input, single program transport stream (SPTS) streams are multiplexing (referred to herein as muxing) together into a single output stream, the incoming packets need to be rescheduled. According to MPEG, any clock references need to be adjusted for the schedule change. In order to do this, the gateway needs to recover the source clock. Thus, there remains a need for an efficient method and apparatus for removing network jitter from the IP network and recovering the clock in the source.
A multiple program transport stream (MPTS) is an MPEG-2 compliant transport stream that contains multiple programs. MPTS is the bitstream format used by subscriber television providers to deliver multiple programs to end users on the subscriber network. A subscriber network utilizing cable diffusion to set-top devices located at subscriber locations, typically includes a headend system from which the transport streams originate, and distribution hub systems located between the headend system and individual subscribers.
The programs contained in the MPTS may have different time bases. The bundling of multiple programs into MPTS can be performed either at the headend of the network or at the distribution hubs. For on-demand content, such as video on demand (VoD), remultiplexing (referred to herein as remuxing) is typically performed at the distribution hubs. For digital broadcast television channels, the multiplexing is normally performed at the headend. MPTS allows the use of statistically remuxing, which yields better overall video quality at a lower total bitrate. If digital television broadcast content is delivered to the distribution hub gateway using MPTS, the gateway needs to be able to handle remuxing of MPTS input with other single program transport streams (SPTS) for on-demand content delivery.